Method and apparatus for deforming a flat on parts of metal strip-type tubing while leaving other parts undeformed

ABSTRACT

A method and apparatus for forming metal strip-type tubing suitable for use in heat exchangers. Deforming flats are formed on parts of a first surface and an opposing surface of the tubular passageways in the strip-type tubing while other parts of the tubing are left undeformed. The deformed flats are adapted to be bonded to flat type fin stock for heat exchange applications. The undeformed areas of the tubing are adapted to be bent without a significant pressure drop occurring in the bend area. The apparatus includes means for deforming the flat on the tubular passageways while restraining the edges of the strip-type tubing and further includes means for sequentially engaging and disengaging the deforming means from contact with the tubing.

United States Patent 1 Tranel METHOD AND APPARATUS FOR DEFORMING A FLAT ON PARTS OF METAL STRIP-TYPE TUBING WHILE LEAVING OTHER PARTS UNDEFORMED Lester J. Tranel, St. Louis, Mo.

Olin Corporation, New Haven, Conn.

Filed: May 4, 1972 Appl. No.: 250,250

Inventor:

Assignee:

Field of Search ..113/118 R, 118 B, 113/118 V, 118 D; 29/1573 V, 157.3 B

References Cited UNITED STATES PATENTS 7/1965 Schaus ..72/191 10/1966 White ..29/157.3V

[451 May 29, 1973 1,649,922 11/1927 Paull ..29/159R FOREIGN PATENTS OR APPLICATIONS 702,086 1/1965 Canada ..29/l57.3 V

Primary Examiner-Richard J. Herbst Attorney- Robert H. Bachman and Gordon G. Menzies [5 7] ABSTRACT A method and apparatus for forming metal strip-type tubing suitable for use in heat exchangers. Deforming flats are formed on parts of a first surface and an opposing surface of the tubular passageways in the striptype tubing while other parts of the tubing are left undeformed. The deformed flats are adapted to be bonded to flat type fin stock for heat exchange applications. The undeformed areas of the tubing are adapted to be bent without a significant pressure drop occurring in the bend area. The apparatus includes means for deforming the flat on the tubular passageways while restraining the edges of the striptype tubing and further includes means for sequentially engaging and disengaging the deforming means from contact with the tubing.

5 Claims, 10 Drawing Figures PATENIED MAY 2 9 I973 SHEET 2 OF 4 This is a division of application Ser. No. 119,600, filed Mar. 1, 1971.

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for forming metal tubing suitable for use in applications, such as condensers for automobile air conditioners. The tubing'produced by this method is also part of this invention.

In companion application Ser. No. 122,607, filed of even date herewith, and assigned to the assignee of the instant invention, there is disclosed a process which comprises taking metal tubing in the form of strip having a plurality of substantially parallel, inflated, longitudinally extending, tubular passageways and flattening a first surface and an opposing surface of the tubular passageways to create more contact area between flat type fin stock and these surfaces. The flattening is generally accomplished by passing the metal strip-type tubing between a deforming means such as rolls which are spaced apart an amount less than the diameter of the tubular passageways while simultaneously restraining the edges of the strip in order to provide adequate tube heights. When the tubing produced by the process of the companion application is bent into a desired configuration, there is some degree of collapse in the tube heights in the bend areas. This collapse in the tube heights causes a pressure drop in the area of the bond. The degree of pressure drop experienced can be tolerated for most applications, for which the tubing in accordance with the companion application is quite suitable without modification. However, where the pressure drop is of concern, the instant invention may be employed.

' SUMMARY OF THE INVENTION In accordance with this invention, a first surface and an opposing surface of the tubing in the bend area is not flattened. In order to accomplish this, a skip flattening technique has been developed. Therefore, in accordance with the process of this invention, the metal strip-type tubing is flattened except in the areas where the bends are to be made. This is accomplished by withdrawing the deforming means from contact with the strip in the bend area. This action takes place automatically in a timed sequence as will be discussed in further detail hereinafter.

The apparatus in accordance with this invention is highly novel in that it includes means for sequentially engaging and disengaging the deforming means into and out of contact with the metal strip-type tubing.

It is accordingly an object of this invention to provide a process for flattening a first surface and an opposing surface of the tubular passageways in a metal strip-type tubing while leaving the bend areas unflattened.

It is a further object of this invention to apply this process to long lengths of strip and to automatically sequence the process to provide unflattened areas at desired intervals along the strip.

It is a further object of this invention to provide composite metal strip-type tubing and heat exchanger having at least one and preferably a plurality of tubular passageways wherein each tubular passageway has a first surface and an opposing. surface flattened in parts and unflattened in. other parts and wherein the unflattened parts correspond to bent areas whenthe tube is fabricated into the heat exchanger.

It is a still further object of this invention to provide an apparatus for flattening a first surface and an opposing surface of the tubular passageways in a metal striptype tubing while retaining unflattened surfaces at intervals spaced apart a desired amount.

Other objects and advantages will become apparent to those skilled in the art as a detailed discussion of particular embodiments proceeds with reference to the drawings which form a part hereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view illustrating the process for forming the sheet metal strip-type tubing preferably employed with this invention.

FIG. 2 shows a perspective view of a sheet metal strip-type tubing having fully inflated tubular passageways therein, which is the preferred starting material in the process of the instant invention.

FIG. 3 shows a perspective view of a sheet metal strip-type tubing in accordance with this invention having a plurality of tubular passageways which have a first surface and an opposing surface flattened in parts and unflattened in another part which corresponds to a bend area.

FIG. 4 is a perspective view of a typical condenser application of the tubing produced by the instant invention.

FIG. 5 is a front view of an apparatus in accordance with this invention.

FIG. 6 is a series of cross sectional views of alternative roll configurations useful with this invention.

FIG. 7 shows perspective views illustrating a modular I embodiment of the flattening rolls useful with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and especially to FIG. 1, there is illustrated a composite metal strip 1 which is used to form the preferred starting material for this invention. The strip 1 may be fabricated by the method disclosed in US. Pat. No. 2,690,002, granted to Grenell on Sept. 28, 1954. While this invention will be described with reference to sheet metal strip-type tubing, it is broadly applicable to most types of strip-type tubing.

Referring to FIG. 1, a pattern of weld-inhibiting or stop-weld material 2 is applied to a clean surface of a first strip 3 of metal. A second strip of metal 4 having a clean surface is superimposed on the surface of the first strip 3 as shown and the two strips are secured together to prevent relative motion therebetween.

Thereafter, the two superimposed strips 3 and 4 are pressure welded together as by rolling so that the adjacent areas 5 of the strip 1 which are not separated by the stop-weld material become bonded together. The rolling of the strips 3 and 4 results in reducing their thickness and in elongating the resulting strip 1 in the direction of rolling while the width of the strip 1 remains substantially the same as the initial width of the strips 3 and 4.

Following the rolling operation, the resultant strip 1 is usually softened, as by annealing, to make it more pliable. If desired, it may be further rolled to the final gage and again softened, as by annealing. The stop-weld material results in the retention of unwelded portions 6 corresponding to the stop-weld pattern 2 which are sandwiched between the outer surfaces of the strip 1.

After softening the strip 1, the unwelded portions 6 are usually expanded to obtain the inflated strip as shown in FIG. 2 having passageways 7. The inflated passageways 7 have a generally cylindrical shape. The expansion is obtained by injecting a fluid, such as air, water or oil under pressure of sufficient magnitude such as 500 to 4,000 psi to permanently deform the strip 1 in the area of the unwelded portions 6 to form the desired passageways 7.

It is preferred that the inflation be carried out under tension in accordance with the teachings of U.S. Pat. No. 3,538,577, granted Nov. 10, 1970, to M.P. OMalley, and assigned to the assignee of the instant invention.

The pattern of weld-inhibiting material may be formed by any desired technique. It is preferred to use the process disclosed in U.S. application Ser. No. 723,055, filed Apr. 22, 1968, by N.A. Keith, and assigned to the assignee of the instant invention.

The weld-inhibiting material itself may be any of the various conventionally used materials such as graphite or titanium dioxide based stop-weld compositions.

The process disclosed in U.S. application Ser. No. 7,729, filed Feb. 2, 1970, now U.S. Pat. No. 3,659,326, granted May 2, 1972, by N.A. Keith, and assigned to the assignee of the instant invention is further illustrative of the processes which may be used to obtain the sheet metal strip for inflation into the tubing useful with this invention. As disclosed therein, the strip may initially be formed as part of a wide sheet which is later slit into strip-like material which may be coiled for further use.

It is to be understood that the above described methods of forming the sheet metal strip-type tubing useful with this invention are only exemplary and that other methods may be employed in the manufacture of the strip. The strip material made by the processes disclosed above or other suitable processes is usually employed in very long lengths. Further, the strip-type tubing may contain any desired number of tubular passageways of any desired diameter, as may be required for achieving given flow and heat transfer rates.

In accordance with the instant invention a strip-type tubing 1' is produced as shown in FIG. 3, preferably in very long lengths, wherein the tubular passageways 7 have flattened surfaces 8 in some areas to which flat type fin stock is to be affixed and unflattened surfaces 9 in other areas where the tubing is to be bent.

In FIG. 4, there is illustrated an application of the tubing 1' produced in accordance with this invention. As shown therein the tube 1' has been bent in a serpentine configuration and flat fin stock 10 has been affixed to the tubing 1' between adjacent passes 11 at areas where the tubing has been flattened 8. The affixing of the flat fin stock 10 is commonly done by means of brazing or soldering so that a bond of good heat transfer qualities is obtained. The fin stock 10 is therefore bonded to the flattened surfaces 8 of adjacent passes 11.

If the metal strip-type tubing 1 of FIG. 2 were employed in the configuration of FIG. 4, there would be insufficient contact between the tubing 1 and the fin stock 10 to obtain adequate heat transfer properties. Therefore, it is necessary to increase the contact area between the fin stock 10 and the tubing 1 as by roll flattening.

In companion application Ser. No. 122,607, a suitable method for flattening the tubing 1 is disclosed. As pointed out therein, it is necessary to restrain the edges of the tubing 1 during the flattening operation, in order to prevent a severe reduction in tube height.

Referring again to FIG. 3, there is shown a metal strip-type tubing 1' processed in accordance with this invention. The tubing comprises a plurality of passageways 7. A first portion 8 of the tube length has been flattened to provide surfaces for the affixation of fin stock 10, a second portion 9 of the tubing length has been left in its original form and a third portion 8' of the tubing has also been flattened for the affixation of fin stock. The tubing shown in FIG. 3 is adapted to be bent in the region which has not been flattened. When the tubing is bent, there is no great pressure drop in the bend area due to a decrease in the tube height in the bend areas since the decreased tube heights are still about the same as the tube heights in the flattened areas. In accordance with this invention, the flat surfaces are generally obtained by rolling while restraining the edges of the metal strip-type tubing 1 to prevent an increase in the width of the tubing. The tubing 1 obtained by this method has the desired flattened surfaces 8 with a small but generally acceptable reduction in tube height. The cross section of the tube 1' as shown in FIG. 3 reveals that the tubular passageways 7 have been substantially squared up. The passageways generally have what may be described as a polyhedral cross section. The polyhedron usually appears as a six sided figure with the sides 8 which contact the fin stock being wider than the adjoining sides S.

The diameter of the tubular passageways 7 in the metal strip may be as desired to meet a given application. However, for condenser applications, it has been found that a diameter between about 0.175 inch and 0.250 inch is most useful with a preferred range between about 0.200 inch and 0.230 inch. Generally, there is a reduction of between 0.020 inch and 0.060 inch in the tube height following inch roll flattening in accordance with this invention. Preferably, the reduction in tube height is between 0.040 inch and 0.050 inch. The width of the flat formed on the tube varies with the tube diameter and the amount of reduction in tube height. For the preferred tube diameter of 0.230 inch, a reduction in tube height of 0.020 inch and 0.060 inch will generally yield a flat having a width between 0.075 inch and 0.125 inch. Preferably, for this size tubing, the flat is around 0.100 inch.

While the above ranges are specific to tubing especially adapted for use in condenser applications, the invention is broadly applicable to any type of metal striptype tubing having any given diameter of tubular passageways.

The apparatus in accordance with this invention is shown in FIG. 5. The apparatus comprises a frame 20. One of the flattening rolls 21 is rotatably mounted to the frame, the shaft extension 22 being connected to a suitable gear drive (not shown) which are well known in the art. A second flattening roll 23 is rotatably mounted within a movable carriage 24 which has shafts 25 which pass through the frame 20. The carriage is spring biased at 26 with respect to the frame 20 so that sufficient pressure is applied to the roll 23 to perform the flattening. The eight of the roll 23, and thereby the distance between the flattening rolls is adjusted by means of nuts 27 which may be tightened or loosened about the threaded shafts 25. As with the other flattening roll 21, this roll 23 has a shaft 28 extending out from the frame which is connected to a suitable gear mechanism (not shown). The hole 29 in the frame 20 through which the shaft 28 passes is elongated to provide for travel of the roll 23.

The apparatus of FIG. 5 also includes edge guides in the form of rolls 30 and 31. Theedge guide roll 30 is rotatably mounted to the frame 20. The roll 31 is held within a movable carriage 32 which moves within a hole in the frame 20. The carriage 32 has flanges 33 with holes which pass about threaded shafts 34 mounted to the frame 20. Spring biasing 3S and nuts 36 are used to provide adjustment of the distance between the edge guide rolls 30 and 31.

The apparatus discussed thus far is substantially the same as the apparatus employed in the companion application. In accordance with this invention, however, a pneumatic or air cylinder 40 type actuator is mounted to the frame 20 and connected to the movable carriage 24. A compressor 41 provides a supply of compressed air for actuation of the air cylinder 40. When the air cylinder 40 is actuated, the carriage 24 is raised and, thereby, the flattening roll 23 is withdrawn from contact with the tubing. A solenoid type valve 42 is placed in the air line 43 to control the operation of the air cylinder 41. A timer 44 controls the actuation of the solenoid valve 42. When the solenoid valve 42 is open, the air cylinder 41 is actuated and the flattened roll 23 is withdrawn from contact with the tubing 1'. When the solenoid valve 42 is closed, the air cylinder 41 is not actuated and the roll 23 contacts the tubing 1 and the apparatus performs as in the companion application. The timer is of a sequential type which permits the solenoid valve 42 to be opened for a specified period and closed for a specified period. The length of time the solenoid valve 42 is closed governs the length of the roll flattened region in the strip. The length of time the solenoid valve is open'govern's the length of the region in the strip which is not flattened and which is later to become a bend area.

To form the strip for use in a serpentine configuration, the sequence is repeated with a given time allowed for each of the flattened passes and a given time allowed for each of the bend areas. For other more complicated heat exchange shapes, more complicated sequencing may be required. This sequencing may be obtained by a timer as shown or by any other method as,

for example, the use of cams or even the use of a computer typ'e device.

In using the apparatus, the distance between the edge guides 30 and 31 is adjusted to substantially equal the width of the starting metal strip-type tubing 1. The distance between the flattened rolls 21 and 23 is adjusted to give the desired amount of flattening. Then the strip 1 of the type shown in FIG. 2 is fed into the apparatus. The emerging strip 1 from the apparatus is of the type shown in FIG. 3.

The apparatus shown in FIG. 5 is but one configuration that may be used. The specific design of the mill itself, other than the roll configuration, the air cylinder type actuater, the strip edge restraining means and the sequencing means, is conventional and forms no part of the invention herein.

The apparatus of FIG. 5 is merely illustrative of one apparatus which could be used. Other means for moving the flattening roll 23 in and out of contact with the tubing 1 could be employed such as, for example, the use of a direct acting cam or other suitable means as are known in the art. It is essential merely that some means be included in the flattening apparatus for sequentially engaging and withdrawing the flattening means into and out of contact with the tubing.

In the apparatus of FIG. 5, the flattening rolls 21 and 23 were of a simple cylindrical shape and, therefore, edge guides 30 and 31 were required as aforenoted to restrain the strip 1 edges to maintain adequate tube heights. Other roll shapes could be used which would eliminate the need for edge guides.

In FIG. 6A, there is shown a roll configuration wherein the upper flattening roll 50 has deep flanges 5 1 between which the metal strip-type tubing 1' rides. These flanges 51 act in the same manner as the edge guides 30 and 31 in the apparatus of FIG. 5. The bottom flattening roll 52 has a width which is adapted to fit between the flanges 51 of the upper flattening roll 50. In operation, the flanges 51 of the upper flattening roll 50 restrain the edges of the metal strip-type tubing while the hub surface 53 of the upper flattening roll 50 coacts with the surface 54 of the lower flattening roll 52 to provide the flattening action.

In FIG. 6B, a still more preferred embodiment is shown. In this embodiment, both flattening rolls 60 are identical and each has flange portions 61. Opposing flange portions 61 clamp the edge of the metal striptype tubing 1' as it is being flattened between the hub portions 62. The engagement between the flanged portions 61 of the flattening rolls 60 and the edges of the strip-type tubing 1' provides the restraining action required in accordance with this invention. However, because only the outer edges of the strip-type tubing 1' are clamped, tliere tends to be a greater squaring up of the outer tubes 63 as compared to the inner ones 64. To overcome this effect, the rolls of FIG. 6C were designed.

In the configuration of FIG. 6C, both rolls are identical and each roll has flange portions 71 which clampingly engage each of the welded portions 72 of the composite metal strip-type tubing 1. In this manner, each of the tubular passageways is squared up substantially the same amount.

The alternative embodiments for the roll configuration shown in FIGS. 6A through 6C could be made in one piece as is common in the art, or it could be assembled from a plurality of pieces in a manner similar to the assembly in slitting knives used in the slitting art. In accordance with this aspect of the invention, the flattening rolls are assembled from a plurality of disks 70 on a shaft 71 having a key way 72 as shown in FIG. 7A. Each disk 70 as shown in FIG. 7B is cylindrical in nature and has a hole 73 of a diameter adapted to fit about the shaft 71. Each disk 70 further has a key-type protrusion 74 extending into the hole and adapted to engage the key way 72 of the shaft 71.

As shown in FIG. 7A, taking the configuration of FIG. 6B as an example, the flange portions 61 could comprise disks 70 of a different diameter than the hub portion 62. The width W of the hub portion 62 could be varied by increasing or decreasing the number of disks 70 present in it. One could obtain the configuration of FIG. 6C by merely inserting further disks 70 of larger diameter at the appropriate positions along the hub portion 62. This approach of using cylindrical disks 70 to form the desired roll configuration is preferred because of the flexibility it gives in changing from one width of strip 1 to another and from one diameter tubing to another, and in changing between strip having different numbers of passageways.

In the embodiment discussed thus far, the flattening of the metal strip-type tubing was obtained by means of roll deforming. However, the flats could be obtained by other methods of deforming the surface as, for example, by compressing the strip in a press or by swaging the strip or hammering the flats. The essential element, however, is that some means must be included in any apparatus for restraining the edges of the strip so that the strip width cannot increase as the tubular surfaces are flattened. The embodiments discussed employing roll deforming, however, are the most preferred and economical approach toward carrying out the instant invention.

Sheet metal strip-type tubing shown in FIG. 2 is preferred as the starting materialof this invention. The invention, however, is broadly applicable to any type tubing including extruded type tubing having a shape similar to that of the tubing of FIG. 2.

The tubing is generally formed of steel, copper, copper alloys, and preferably, aluminum or aluminum alloys.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are suitable of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within the spirit and scope as defined by the claims.

What is claimed is: v

1. A process of forming a metal strip-type tubing adapted to be used in a heat exchanger said tubing having edges comprising: providing a metal strip-type tubing having a plurality of tubular passageways; deforming a flat on parts of a first surface and an opposing surface of said plurality of tubular passageways, while leaving other parts of said first surface and said opposing surface undeformed, and simultaneously restraining the edges of said metal strip-type tubing to prevent said tubing from increasing in width.

2. A process as in claim 1 wherein said deforming step is carried out in a timed sequence, said timed sequence comprising:

A. deforming a first part of said strip during a first time interval to obtain said deformed flat surfaces;

B. leaving undeformed a further part of said strip during a second time interval; said timed sequence A and B being repeated as desired to obtain strip adapted to be formed into a desired heat exchange configuration.

3. A process as in claim 2 further including forming said tubing into a serpentine configuration having a plurality of passes and bend areas with the tubing in each of said passes having said deformed flats and tubing in said bend are as being undeformed.

4. A process as in claim 3 wherein said strip-type tubing is formed of at least two strips of metal pressure welded together in parts.

5. A process as in claim 4 wherein said deforming is performed by passing said strip between a pair of spaced apart rolls. 

1. A process of forming a metal strip-type tubing adapted to Be used in a heat exchanger said tubing having edges comprising: providing a metal strip-type tubing having a plurality of tubular passageways; deforming a flat on parts of a first surface and an opposing surface of said plurality of tubular passageways, while leaving other parts of said first surface and said opposing surface undeformed, and simultaneously restraining the edges of said metal strip-type tubing to prevent said tubing from increasing in width.
 2. A process as in claim 1 wherein said deforming step is carried out in a timed sequence, said timed sequence comprising: A. deforming a first part of said strip during a first time interval to obtain said deformed flat surfaces; B. leaving undeformed a further part of said strip during a second time interval; said timed sequence A and B being repeated as desired to obtain strip adapted to be formed into a desired heat exchange configuration.
 3. A process as in claim 2 further including forming said tubing into a serpentine configuration having a plurality of passes and bend areas with the tubing in each of said passes having said deformed flats and tubing in said bend are as being undeformed.
 4. A process as in claim 3 wherein said strip-type tubing is formed of at least two strips of metal pressure welded together in parts.
 5. A process as in claim 4 wherein said deforming is performed by passing said strip between a pair of spaced apart rolls. 